Any jet aircraft pilots out there? Especially small jet’s like the old Douglas A4.
My question is, when you change attitude such as pitch up or down or go into a turn does the engine rotor produce a noticeable gyroscopic force on the plane?
I got to thinking about this after having watched a program on WWI fighters that used rotary engines. In this engine, the crankshaft is stationary and everything else on the engine rotates. This produced a large gyroscopic torque that made the plane difficult to fly especially at low speeds on landing and takeoff when control was marginal anyway.
I’m not a jet pilot, but being an aviator, I guess I’m confused as to how the compressor blades could possibly produce any kind of gyroscopic force. Props produce this (or, in the case of those older planes, whatever’s spinning). I’m not aware of any jet engines which do. Besides, even if there was some very small force produced, most jet aircraft have two engines, which takes any such force off the longitudinal axis, which I’d think decreases any gyroscopic effects.
Anything that spins produces centripetal force, so I’m sure the fan discs in jets make fine gyroscopes.
It was a problem even for more modern prop planes. I know that 2/4 engine prop planes had pairs of enginrs rotating in opposite directions to cancel out the effect.
Any rotating mass is a gyroscope, on axis or off. The rotor of a turbojet engine is a rotating mass. Ergo, the rotor of a turbojet engine is a gyroscope.
Most two (reciprocating) engine planes have propellors that rotate in the same direction. The only one I am aware of that had contrarotating props was the Lockheed P-38.
Most multiengine planes used air cooled radial engines that had operating RPM such that they were direct drive. I.e. the prop was directly attached to the crankshaft. Counter rotating props would have meant engines that turned in the opposite directions. Too much of a logisitical headache for the small gain of making things easier on the pilot.
Yes, jet engines do produce a measurable and calculable gyroscopic moment, in proportion to the rate at which the axis is changing. In all the mount load calculations I’ve done on them, though, it’s been a pretty small effect compared to the maneuver loads themselves.
There may have been a greater effect with earlier engines, which had much heavier rotors. The A-4 you mentioned, especially, is pretty small compared to the rotor sizes.
I was thinking more about the effect on control and not journal loads. Such as would be the case in a “go around” on a carrier landing. The airspeed is relatively low and the engine is turning max RPM. Is it a big enough problem the pilot must watch for it?
I remember the pictures of the F-14 crash where the pilot tried to go around because of a missed approach and the plane pulled hard left and crashed into the sea.
Ok, I wasn’t thinking too clearly. I also had my brain wrapped around control issues, and I’ve never heard of gyroscopic precession applied to jets.
David, I’m not sure what crash you’re talking about. But I’ve never heard of any crash which had gyroscopic loads as a contributing factor. My guess for the Tomcat crash is either mech malfunction or pilot error, as in a power-on stall.
I’ve never, never had that happen to me (heh heh).
It was the well publicized crash of a woman pilot in an F-14. I expect you are right. If the pilot realized a bad situation too late and pulled up too hard a high-speed stall could easily result in what the pictures showed.
The documentary about the gyro action in old planes, like the Sopwith Camel, just got me thinking. But they were boxkites, the Camel had a bad weight and balance problem (from what the program said) and apparently none of the planes of that time could be trimmed to fly “hands-off” for any flight condition. One advantage of the gyro was that you could make a really tight turn in the direction it wanted you to go.